southern california alluvial scrub habitats -...

ClimatechangevulnerabilityassessmentfortheSouthernCaliforniaClimateAdaptationProject.CopyrightEcoAdapt2017.

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SouthernCaliforniaAlluvialScrubHabitatsClimateChangeVulnerabilityAssessmentSynthesis

AnImportantNoteAboutthisDocument:Thisdocumentrepresentsaninitialevaluationofvulnerabilityforalluvialscrubhabitatsbasedonexpertinputandexistinginformation.Specifically,theinformationpresentedbelowcompriseshabitatexpertvulnerabilityassessmentsurveyresultsandcomments,peer-reviewcommentsandrevisions,andrelevantreferencesfromtheliterature.Theaimofthisdocumentistoexpandunderstandingofhabitatvulnerabilitytochangingclimateconditions,andtoprovideafoundationfordevelopingappropriateadaptationresponses.

ExecutiveSummaryInsouthernCalifornia,alluvialscrubhabitatsarecommonlylocatedinoutwashfansandriverinedepositsatcanyonmouthstowardthebaseofmountainranges,includingtheSanGabriel,SanBernardino,SanJacinto,andSantaAnaranges(Hanesetal.1989;SaffordandQuinn1998).Alluvialscrubhabitatscanalsobefoundonwashdepositsofrivers(Hanesetal.1989),includingtheSantaAnaRiveranditstributaries.Alluvialscrubconsists

mainlyofflood-adapteddrought-deciduoussubshrubsandevergreenwoodyshrubs(Hanesetal.1989).TherelativevulnerabilityofalluvialscrubhabitatsinsouthernCaliforniawasevaluatedtobemoderate-high1byhabitatexpertsduetomoderate-highsensitivitytoclimateandnon-climatestressors,highexposuretoprojectedfutureclimatechanges,andmoderateadaptivecapacity.

SensitivityandExposure

Climatesensitivities:Precipitation,snowpackdepth,snowmelttiming,flowregimes(highandlowflows),soilmoisture,drought,airtemperature,extremelowtemperatureeventsDisturbanceregimes:Flooding&erosion,wildfireNon-climatesensitivities:Dams&waterdiversions,invasive&problematicspecies

Alluvialscrubhabitatsarecriticallysensitivetoclimatedriversanddisturbanceregimesthatalterhydrologic,flooding,andscouringregimesand/orthataltermoistureavailability,asthesefactorsaffecthabitatdistribution,composition,andsurvival.Otherfactors(e.g.,temperature,wildfire)arealsolikelytoaffectvegetationandassociatedwildlifecommunities.Alluvialscrubhabitatsarealsoverysensitivetonon-climaticdriversthatexacerbateclimate-drivenchanges.Forexample,damsandwaterdiversionscompoundhydrologicalshifts,andinvasivespeciescandirectlycompetewithalluvialscrubvegetationforincreasinglylimitedresources.

AdaptiveCapacity

Habitatextent,integrity,andcontinuity:Low-moderategeographicextent,lowintegrity(i.e.,degraded),low-moderatecontinuityResistanceandrecovery:Moderateresistance,moderate-highrecoverypotential

1Confidence:High

PhotobyArleeMontalvo/RCRCD-USFS-PSW(PublicDomain)


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Habitatdiversity:Low-moderateoveralldiversityManagementpotential:Moderate-highsocietalvalueandmanagementpotential

Largeportionsofalluvialscrubhabitathavebeenlostasaresultofhumanactivity,resultinginisolatedhabitatpatchesalongunalteredstreamsandalluvialoutwashes.Avarietyoflandscapebarriers,inadditiontothesoilrequirementsofcomponentvegetation,limithabitatconnectivityandmayreducealluvialscrubdispersalopportunitiesinresponsetoclimaticstressors.However,alluvialscrubcommunitiesaredisturbance-adaptedandfeaturemoderatediversity,whichmayenhancetheirresilienceinthefaceofclimatechange.Alluvialscrubhabitatsprovideavarietyofecosystemservices(e.g.,biodiversity,floodanderosionprotection).Potentialmanagementoptionsidentifiedbyhabitatexpertslargelydealwithmaintaininghydrologicalregimesinexistinghabitatsandminimizingnon-climaticstressors(e.g.,invasivespecies,development/alterationofexistinghabitat).

SensitivityTheoverallsensitivityofalluvialscrubhabitatstoclimateandnon-climatestressorswasevaluatedtobemoderate-highbyhabitatexperts.2

Sensitivitytoclimateandclimate-drivenchangesHabitatexpertsevaluatedalluvialscrubhabitatstohavemoderate-highsensitivitytoclimateandclimate-drivenchanges,3including:precipitation,snowpackdepthandsnowmelttiming,flowregimes(highandlowflows),soilmoisture,drought,andairtemperature(includinglowtemperatureevents).4Alteredhydrology(soilmoisture,precipitation,snowpack,drought,5flowregimes)Soiltextureandsubsurfacemoistureinfluencealluvialscrubspeciescompositionanddistribution(Hanesetal.1989).Forexample,annualprecipitationtypicallyincreaseswithelevation,andfieldstudieshaveshownpioneeralluvialscrubspeciestobeassociatedwithlowerelevationsandlessannualprecipitationandintermediateandmaturealluvialscrubplantcommunitiestobeassociatedwithhigherelevationsandhigherannualprecipitation(Buck-Diazetal.2011).Increasedmoisturedeficitsassociatedwithclimatechangemaypreventsuccessiontomaturevegetation(Hanesetal.1989)and/orcauseconversiontomorexericplantcommunities(e.g.,coastalsagescrub),particularlyinareasfartherfromthestreamchannelthatareinundatedlessfrequently(Smith1980).Shiftsinprecipitationandhydrologicalchangesarealsolikelytoimpacttheabundance,germination,andseedproductionofannualspeciespresent(Allen1996;Harris1987;Sclafani2013).Forexample,lowprecipitationyearsmayreduceabundanceandestablishmentofnativeannualssuchastheslender-hornedspineflower(Dodecahemaleptoceras),whilehighprecipitationyearsmayfavorestablishmentandresultin

2Confidence:High3Confidence:Moderate4Factorspresentedarethoserankedhighestbyhabitatexperts.Afulllistofevaluatedfactorscanbefoundattheendofthisdocument.5Habitatexpertsidentifieddroughtasaclimatestressor,butdidnotprovideanyadditionalcomments,andnosupportinginformationcouldbefoundintheliterature.


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populationincreases(Allen1996;Sclafani2013).Similarly,reducedannualprecipitationmaynegativelyaffectcryptobioticsoilcrustspecies,whichflourishduringwetperiods(Jigouretal.2001).Alluvialscrubcommunitiesareadaptedtoperiodicflooding(Hanesetal.1989)duetoseasonalsnowmelthydrographpeaksaswellasshort,high-volumeprecipitationeventscharacteristicofsouthernCalifornia(SaffordandQuinn1998;WoodandWells1996).Changesinprecipitation,snowpack,andsnowmelttimingarelikelytointeractwithhumanwatershedmanagementtoaffectsoilmoisture,flowvolumes,andscouringandsedimentationregimes,whichmayaffectthesuccession,composition,andpersistenceofalluvialscrubvegetation(Hanesetal.1989;Harris1987;Harvey2002).Forexample,reducedfloodfrequencyduetoclimate-orhuman-drivenchangesinhydrologicregimesmayhomogenizealluvialscrubstandageandstructurebyreducingthenumberofearlyseralcommunities(U.S.FishandWildlifeService2009;WesternRiversideCounty(WRC)2003),degradinghabitatvalueforwildlife(U.S.FishandWildlifeService2009).TemperatureTemperatureinfluencesalluvialscrubspeciescomposition(Buck-Diazetal.2011;Orretal.2011),establishment(Haner1984),andsurvival(Sclafani2013).Forexample,hotconditionscanpreventalluvialscrubestablishment(Haner1984)andregeneration(Smith1980).Thediverseassociationsofalluvialscrubcommunitiescontributetovariabletemperaturesensitivity.Forexample,somealluvialscrubspecies(e.g., Lepidospartumsquamatum) exhibitwinterdormancy,whichmayallowthemtosurvivefreezingperiods.Bycontrast,otheralluvialscrubassociateshavewintergrowthperiods(e.g.,Eriogonumfasciculatumvar.foliolosum,E.f.var.polifolium,Artemisiacalifornica)orarecommonassociatesofcoastalsagescrub(i.e.aremoreadaptedtomildtemperatures),whichmaymakethemmoresensitivetocoldevents(VulnerabilityAssessmentReviewers,pers.comm.,2015).Overall,shiftsinminimumwintertemperaturesarelikelytoaffectthedistributionandspeciescompositionofalluvialscrubvegetation(VulnerabilityAssessmentReviewers,pers.comm.,2015),andincreasinglywarmconditionsmayalterestablishmentandmortalitypatterns(Haner1984;Smith1980).Increasingannualtemperaturesmayalsoimpactalluvialscrubcommunitiesbydrivingshiftsfromsnowtorain(Hayhoeetal.2004;Sunetal.2015),whichwilllikelycausehydrologicalalterationsinthishabitat(VicunaandDracup2007).SensitivitytodisturbanceregimesHabitatexpertsevaluatedalluvialscrubhabitatstohavelow-moderatesensitivitytodisturbanceregimes6,including:floodinganderosionandwildfire.7Diseaseandwindalsoshapethishabitat,buttoalesserdegree(VulnerabilityAssessmentReviewers,pers.comm.,2015).

6Confidence:Moderate7Factorspresentedarethoserankedhighestbyhabitatexperts.Afulllistofevaluatedfactorscanbefoundattheendofthisdocument.


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FloodinganderosionAlluvialscrubisadaptedtoinfrequentbutsevereflooding,erosion,andsedimentationevents(Hanesetal.1989;Smith1980),whichdelivernewnutrientsandorganicmatter,redistributesediments,andfacilitatesuccessionandspatialdiversitywithinalluvialscrubhabitat(Hanesetal.1989;Jigouretal.2001;KirkpatrickandHutchinson1977;SaffordandQuinn1998;Wirka1997andcitationstherein).Severalimportantalluvialscrubspeciesareresilienttofloodshearandcanrecolonizesedimentsfromseveredrootsandrhizomes(e.g.,Eriodictyonspp.,L.squamatum),butmanyspeciescolonizefreshsedimentsfromseed(Sclafani2013;forfurtherdiscussion,seeResistanceandRecoverysectionbelow).Differentsetsofspeciestendtocolonizeandpersistinsedimentsofdifferentagesandcompositionswhichresultsinadiversesetofalluvialscrubplantcommunities(Hanesetal.1989;Smith1980).Thelocationandcompositionofsubstrateswithinfloodplainsdependsonmanyfactors(Haner1984).Channelmorphology,slope,ageandtypeofparentmaterials,floodfrequency,floodvelocity,flooddepthandpresenceofvegetationislandsinteracttoinfluencehowdifferentparticlesizessortthemselvesoutacrossthefloodplain.Subsequentsurfaceerosion,includingwinderosion,providestheopportunityfordepositionandincorporationoffineparticles(includingorganics)downwardintotheinitiallyporous,typicallysandy/gravelysubstrates(Haner1984;Hanesetal.1989;SaffordandQuinn1998;Smith1980;WoodandWells1996).Recognizablezoneswithdifferentdisturbanceregimesandsubstratequalitiesformacrossfloodplainsandhavebeenexaminedforassociationswiththeirvegetationcommunities(e.g.,seeBarbourandWirka1997,Burketal.2007,Hanesetal.1989,Smith1980),anddifferentcombinationsofplantstendtooccupythedifferentzones.Forexample,floodingduring1938and1969insouthernCaliforniacreateddistinctterracesalongstreamchannels,whichnowfeaturevarioussuccessionalspeciesassemblages(Hanesetal.1989;Smith1980).Althoughalluvialscrubcommunitiesareadaptedtoflooding,prolongedinundationandaccumulationofsiltandclayparticlesasaresultoflandscapeandhydrologicalalterationscanleadtothecolonizationanddominanceofdifferentplantcommunities(e.g.,moremesicspecies;Burketal.2007;Jigouretal.2001).Alluvialscrubsoilsdrainfairlyquickly,butdikes,damsandotherfeaturesslowrunoff,constrainflows,andchangethepatternoffloodsimportanttorejuvenationofalluvialscrubplantcommunities(BarbourandWirka1997;Burketal.2007;Hanesetal.1989).WildfireFireresetsalluvialscrubsuccession,altersspeciescomposition,andreleasesnitrogen,whichfacilitatesfertilization(SaffordandQuinn1998),butfinerdetailsregardingthefrequencyandtheroleoffireinalluvialscrubmaintenanceanddevelopmentarenotwellunderstood(WRC2003).Manyalluvialscrubspeciesarefire-adapted;mostofthecommonshrubsandsubshrubsinalluvialscrubcommunitiesarefacultativeseeders,andsomecommonannualsgerminatereadilyafterfire(Keeleyetal.2006;Sclafani2013).Analysisofsurveydatafrom2010-11foundthatthehighestfirefrequencywasassociatedwiththeScalebroom(L.squamatum)-Californiabuckwheat(E.fasciculatum)associationrelativetootheralluvialvegetativegroupings,andthelongesttimebetweenfireswasassociatedwiththeL.squamatum-Eriodictyontrichocalyx-


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HesperoyuccawhippleiandL.squamatum/mixedephemeralannualsassociations(Buck-Diazetal.2011).Firemaybelesslikelyinpioneerstandsinthemostrecentlyfloodedzonesduetoreducedfuelavailability(WRC2003).Ingeneral,increasedhumanactivityadjacenttoalluvialscrubstands(e.g.,development)canincreasefirerisk(SaffordandQuinn1998).Shiftingfireregimes,aswellasshiftingfloodregimesandothergrounddisturbance,mayalsonegativelyimpactnativeground-dwellinginsects(Cane1991;Williamsetal.2010),whichalluvialscrubspeciesutilizeforpollinationandseeddispersal(AtallahandJones2003;DeSimoneandZedler1999;Dorsettetal.2001;Hobbs1985;Moldenke1976;MoldenkeandNeff1974;MontalvoandBeyers2010;Sclafani2013).DiseaseRootinfections(e.g.,Phytophthora)thriveundermoistconditions(Swain2002)andmaybemorecommoninalluvialscrubhabitats(e.g.,onfansandupperalluvialterraces)duringsummerstormfloodperiods(VulnerabilityAssessmentReviewers,pers.comm.,2015).Sensitivityandcurrentexposuretonon-climatestressorsHabitatexpertsevaluatedalluvialscrubhabitatstohavehighsensitivitytonon-climatestressors,8withanoverallhighexposuretothesestressorswithinthestudyregion.9Keynon-climatestressorsidentifiedbyhabitatexpertsforalluvialscrubhabitatsincludedamsandwaterdiversionsandinvasiveandotherproblematicspecies.10Habitatexpertsalsoidentifiedland-useconversion,recreation,transportationcorridors,andenergyproductionandminingasnon-climatestressorsforalluvialscrubhabitats.11Thescientificliteratureadditionallysuggeststhatfiresuppressionmayalsoaffectthishabitat.Habitatexpertsevaluatedalluvialscrubexposuretomostnon-climatestressorstobefairlyconsistentacrossthestudyregion,withtheexceptionofrecreationandinvasivespecies;expertsindicatedrecreationimpactsoccurinmorelocalizedareas,andinvasivespecies,thoughpresentthroughoutthestudyarea,exhibitpatchyinvasionofalluvialscrubhabitats(VulnerabilityAssessmentReviewers,pers.comm.2015).Dams,waterdiversions,andfloodcontrolstructuresWaterdemands(includingsurfaceandgroundwaterwithdrawals)andflood-controlprojectsalteralluvialscrubcommunitycompositionandthreatentheintegrityandpersistenceofthishabitattypebyalteringfloodingandscouringregimes,watersupply(Burketal.2007;Hanesetal.1989;Rundel2007;SaffordandQuinn1998;Sclafani2013),andconnectivitytoriverandstreamsystems.Forexample,debrisbasinsinterruptsedimentdeliverytodownstreamhabitats(BonTerraConsulting2010),whichcanalterscourpatternsinalluvialscrubcommunitiesandreducenutrientdeliveryvianewsediment(Hanesetal.1989;Jigouretal.2001).Inaddition,alluvialvegetationthatestablishesinthesedebrisbasinsmayberemovedduringroutinebasinmaintenance(BonTerraConsulting2010).Similarly,streamchannelizationassociatedwith

8Confidence:High9Confidence:High10Factorspresentedarethoserankedhighestbyhabitatexperts.Afulllistofevaluatedfactorscanbefoundattheendofthisdocument.11Notallhabitatexpertsagreedonthesenon-climatestressors.


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waterprojectscancauseavarietyofalterationstonaturalstreamfunctionandprocesses(PaulandMeyer2001;Walshetal.2005),impactingadjacentalluvialscrubhabitats.Currentandplannedwaterinfiltrationareas(e.g.,infiltrationponds),whicharedesignedtocollectwaterforaquiferinfiltration,cansignificantlyalterand/ordisplacealluvialscrubvegetation(SaffordandQuinn1998).Percolationpondsandrelatedinfrastructurecanincreaseandprolonginundationinalluvialscrubcommunities,potentiallyresultinginashifttowardmoremesophyticvegetation,whilstsimultaneouslydecreasingsoilmoistureelsewhereinthealluvialfan,affectingalluvialscrubspeciescomposition(SaffordandQuinn1998).Pondconstructioncanalsophysicallyremovealluvialscrubvegetationandresultinalteredvegetationcommunities(e.g.,ashasoccurredbelowtheSevenOaksDamontheuppermainstemoftheSantaAnaRiver;A.Montalvo,pers.comm.,2015).Infiltrationareasandotherwatercontrolstructurescaninteractwithclimate-drivenshiftsindisturbanceregimestosignificantlyaffectsoilmoistureandalluvialscrubcommunitycomposition(SaffordandQuinn1998).Further,climatechangemayincreasedemandforthesestructures(Tanakaetal.2006).InvasiveandotherproblematicspeciesExoticgrassesandotherinvasivespeciesmayincreasecompetition,reducefitness,and/ordepressabundanceofnativealluvialscrubvegetation,particularlyannuals(Allen1996;SaffordandQuinn1998).Invasivespecieshavebeenintroducedviaagriculture,development,andtransportationcorridors,andcontinuetothreatenthishabitat(SaffordandQuinn1998;Sclafani2013),particularlyundershiftingclimaticconditions(e.g.,shiftingsummerprecipitationpatterns).Invasionsarepatchyindistribution(VulnerabilityAssessmentReviewers,pers.comm.,2015).Transportationcorridors,recreationTransportationcorridorsandrecreation,includingoff-highwayvehicle(OHV)use,cancontributetohabitatfragmentation,degradation,anddisturbance(SaffordandQuinn1998;Sclafani2013).Forexample,transportationcorridorsandassociatedleveesoftenconstrictorfillfloodchannels,alteringnaturalflooding,scouring,andhydrologicalregimes(VulnerabilityAssessmentReviewers,pers.comm.,2015).Transportationcorridorsandillegalrecreationactivitiescanalsofacilitateinvasivespeciesestablishmentanddominance(VulnerabilityAssessmentReviewers,pers.comm.,2015).IllegalOHVusecanunderminenativevegetationrecovery/colonizationinadrierclimatebycompactingsoil(VulnerabilityAssessmentReviewers,pers.comm.,2015).However,somealluvialscrubspeciesmaybeabletocolonizetiretracksandoldroadbeds(Allen1996;SaffordandQuinn1998).LanduseconversionAgriculturalandurbandevelopmenthasdestroyedalargeportionofalluvialscrubhabitat(Allen1996;Hanesetal.1989;Rundell2007;SaffordandQuinn1998;WoodandWells1996)outsideofnationalforestlandsinsouthernCalifornia.Landuseconversioncanalsoactasaphysicalbarriertovegetationdispersal(VulnerabilityAssessmentReviewers,pers.comm.,2015).Urbandevelopmentchangesrunoffandpercolationpatterns,affectingfloodregimesandtheformationoffansandaxialwashes(SaffordandQuinn1998;Scott1973),effectsthat


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willlikelybeexacerbatedunderchangingclimateconditions(alteredfloodingregimes;VulnerabilityAssessmentReviewers,pers.comm.,2015).Pollutionfromresidentialandurbanrunoffcandegradeordestroyalluvialscrubhabitat(WRC2003),andincreasedhumanactivitycanincreasefirerisk(SaffordandQuinn1998).Ingeneral,humandisturbancecanresetalluvialscrubsuccession,interrupthabitatcontinuity,and/orthreatencommunitypersistence(VulnerabilityAssessmentReviewers,pers.comm.,2015).EnergyproductionandminingRockandsandmininginfloodplainalluviumcandestroyalluvialscrubhabitat,removekeysediment(Hanesetal.1989),killcomponentvegetation(Allen1996),andcontributetoestablishmentofnon-nativespecies(Sclafani2013).SouthernCaliforniahasalonghistoryofaggregateandsandmining,includingactivityinTujungaWash(Scott1973),TemescalWash,tributariestotheSantaAnaRiverandmainstem,theupperSantaAnaRiverbelowSevenOaksDam,andbelownationalforestlandinLytleCreek(e.g.,seeCityofRialto2012,SanBernardinoValleyWaterConservationDistrict2008).Desertalluvialscrubhabitatsarealsovulnerabletoshiftingfloodingregimesasaresultofenergyfarms(VulnerabilityAssessmentReviewers,pers.comm.,2015).Frackingmayalsoaffectthishabitatbyremovingwaterfromstreamandriversystems(Bryceetal.2012).FrackingisoccurringintheLosPadresNationalForestandexpandinginLosAngelesCounty(VulnerabilityAssessmentReviewers,pers.comm.,2015).FiresuppressionFiresuppressionhasincreasedoverthelastcenturyinordertoprotectdevelopments.However,suppressionhascontributedtoalteredfuelprofilesinbothalluvialscrubandadjacentvegetationcommunities(chaparral,sagescrub;SaffordandQuinn1998),perpetuatingtheriskofalteredfireregimesunderclimatechange.Inaddition,firesuppressioncancontributetoinvasivespeciesestablishment(VulnerabilityAssessmentReviewers,pers.comm.,2015).

FutureClimateExposureHabitatexpertsevaluatedalluvialscrubhabitatstohavehighexposuretoprojectedfutureclimateandclimate-drivenchanges,12andkeyclimatevariablestoconsiderinclude:increasedairtemperatureanddrought,precipitationchanges,increasedwildfire,decreasedsoilmoisture,andalteredstreamflows(Table1).13Foradetailedoverviewofhowthesefactorsareprojectedtochangeinthefuture,pleaseseetheSouthernCaliforniaClimateOverview(http://ecoadapt.org/programs/adaptation-consultations/socal).Ingeneral,refugiafromchangingclimateconditionsarelesslikelytoexistforalluvialscrubincomparisontoothervegetationtypesbecauseterrainexertsastronginfluenceonthelocationandformationofalluvialdeposits(i.e.,higherelevationsaresteeperandrockierandsupportlessalluvialdeposits;VulnerabilityAssessmentReviewers,pers.comm.,2015).

12Confidence:High13Factorspresentedarethoserankedhighestbyhabitatexperts.Afulllistofevaluatedfactorscanbefoundattheendofthisdocument.


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Table1.Anticipatedalluvialscrubresponsestoclimateandclimate-drivenchanges.

Climateandclimate-drivenchanges AnticipatedalluvialscrubresponseHydrologyVariableannualprecipitationvolumeandtiming;increasedclimaticwaterdeficit;longerandmoreseveredroughtswithdroughtyearstwiceaslikelytooccur;shiftingflowregimes(increasedwinterflow,decreasedsummerflow)

• Alteredspeciescompositionandrecruitment;dryyearsmayinhibitannualplantestablishment

• Alteredsuccessionpatterns;dryconditionsmaypreventsuccessiontomaturecommunities

• Potentialconversiontomorexericsoilsandspeciesifmoisturedeclines

Airtemperature+2.5to+9°Cby2100

• Altereddistribution• Alteredspeciescomposition;freeze-sensitivevegetation

mayhavemoregrowthopportunities,buthotconditionsmayalterannualplantestablishmentandsurvival

• Alteredspeciescompositionandsuccessionpatternsduetorelatedshiftsinhydrology

FloodingregimesIncreasedwinterfloodvolumeandfrequency;reducedspringfloodvolume

• Shiftsinhabitatlocation• Alteredseasonsforcolonization• Alteredsuccessionpatternsandseralstructure;increased

floodingwilllikelypromotehabitatheterogeneity• Alteredspeciescomposition• Alteredpollinationanddispersalduetofloodingimpacts

onnativeground-dwellinginsectsWildfireIncreasedfiresize,frequency,andseverity

• Effectslargelyunknown• Morefrequentfiremayalterspeciescompositionand

impedevegetationrecovery• Alteredpollinationanddispersalduetofireimpactson

nativeground-dwellinginsectsHydrologyShiftsinprecipitation(includingshiftsfromsnowtorain)thatalterfloodregimesandalluvialfanprocesseswilllikelyaffectalluvialscrubvegetationcompositionanddistribution(Harveyetal.2002;SaffordandQuinn1998).Forexample,climaticallyinducedflowregimeshiftsmaycauseheightenedchannelincisionandreducedsedimentation,contributingtoalluvialfanbaselevelchangesandaffectingfanevolutionandcomponentvegetation(Harveyetal.2002).Shiftingflowregimesmayalsochangepatternsofscouranddepositiononaxialwashdeposits,affectingvegetation(Harveyetal.2002).Shiftsinprecipitationtiming,particularlysummerrains,mayalsoalterinvasivespeciescomposition,establishment,anddominanceinalluvialscrubhabitats(VulnerabilityAssessmentReviewers,pers.comm.,2015).Reducedsnowpackandearliersnowmelttimingmayaffecttheseasonaldurationanddepthofintermittentstreamflowsandgroundwaterrecharge,resultinginalteredhydrologyindifferentalluvialareasandaffectingthedistributionandpersistenceofalluvialscrubvegetationcommunities(A.Montalvo,pers.comm.,2015).WildfireShiftsinwildfirefrequencywouldlikelyaffectalluvialscrubspeciescompositionandlong-termpopulationstructure(SaffordandQuinn1998)andfrequentfiresarelikelytobedetrimentalto


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habitatrecovery(VulnerabilityAssessmentReviewers,pers.comm.,2015).Alluvialscrubvegetationassociationsthatfeaturecommonsagescruborchaparralassociateswilllikelyexhibitsimilarresponsestothosehabitattypes(Keeleyetal.2005;seesagescrubandchaparralhabitatsyntheses).

AdaptiveCapacityTheoveralladaptivecapacityofalluvialscrubhabitatswasevaluatedtobemoderatebyhabitatexperts.14

Habitatextent,integrity,continuityandpermeabilityHabitatexpertsevaluatedalluvialscrubhabitatstohavealow-moderategeographicextent(i.e.,habitatisquitelimitedwithinthestudyregion),15lowintegrity(i.e.,habitatisdegraded),16andfeaturelow-moderatecontinuity(i.e.,onlysomehabitatpatchesareconnected).17Habitatexpertsidentifieddamsandwaterdiversions,transportationcorridors,energyproductionandmining,andgeologicfeaturesasbarrierstohabitatcontinuityanddispersalforthisecosystemtype.18InsouthernCalifornia,alluvialscrubhabitatsaremostcommonlyfoundinfloodplainsatcanyonmouthsonthewesternsideoftheSanGabriel,SanBernardino,andSanJacintoranges(Hanesetal.1989;SaffordandQuinn1998),andonallsidesoftheSantaAnaMountains(A.Montalvo,pers.comm.,2015).Alluvialscrubalsogrowsinotherriverine,floodplain,andwashhabitatsthroughoutsouthernCalifornia(Hanesetal.1989).Historically,alluvialscrubhabitatwaswidelydistributedandextensiveinsouthernCalifornia,butavarietyofhumanactivities(e.g.,agriculture,development,mining,damsandwaterdiversions)haveeliminatedamajority(90-95%)ofhistoricalhabitat(Hanesetal.1989;Orretal.2011andcitationstherein;SaffordandQuinn1998;Wirka1997).Currentalluvialscrubhabitatsarefairlyisolated,restrictedonlytounalteredstreamsandalluvialfanoutwashes(Hanesetal.1989;SaffordandQuinn1998;WRC2003),andconnectivityvaries.Forexample,alluvialscrubhabitatispatchybutconnectedalongagivenstreamorrivercourse,butconnectivitybetweendifferentalluvialfansislow(VulnerabilityAssessmentReviewers,pers.comm.,2015).Inadditiontobarriersnotedbyhabitatexperts,alluvialscrubhabitatcontinuityanddispersalmayalsobeaffectedbythesoilrequirementsandvariousdispersalcapabilitiesofdifferentspecies(Allen1996;Hanesetal.1989;SaffordandQuinn1998;Sclafani2013).ResistanceandrecoveryHabitatexpertsevaluatedalluvialscrubhabitatstohavemoderateresistancetoclimatestressorsandmaladaptivehumanresponses,19andmoderate-highrecoverypotential.20Asa14Confidence:High15Confidence:High16Confidence:Moderate17Confidence:Moderate18Barrierspresentedarethoserankedmostcriticalbyhabitatexperts.Afulllistofevaluatedbarrierscanbefoundattheendofthisdocument.19Confidence:Moderate


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disturbance-adaptedcommunity,alluvialscrubmaybefairlyresilientandabletorecoverifgiventimeandspace(SaffordandQuinn1998).Further,componentalluvialscrubspecieshavediversereproductivecapacities,whichmayenhanceoverallhabitatresilience(A.Montalvo,pers.comm.,2015).21Forexample,afterscouringfloods,severalimportantshrubsreestablishreadilyfromextensiverootandrhizomesystems,includingL.squamatum,Eriodictyoncrassifolium,andE.trichocalyx.Malosmalaurinaalsoresproutsafterfloods,butcancolonizereadilyfromseed.Mostofthecommonshrubsandsubshrubsinalluvialscrubarefacultativeseedersandsomeofthecommonannualsgerminatereadilyafterfire(Keeleyetal.2006).Forexample,theEriodictyonspecieshastiny,highlydormantseedsthatgerminatepost-fire(Keeleyetal.2006).UnlikeEriodictyon,L.squamatumseedsareshort-livedandarenotadaptedtofire,buttheseedsdispersebywindinthelatefallandgerminatereadilyinopen,moistsandyalluvium.E.fasciculatumalsoestablishesprimarilyfromseed,butpartiallyburiedplantscansometimesresprout.Severalrareplantsofalluvialscrubestablishonlyfromseeds,includingEriastrumdensifoliumssp.sanctorum,Dodecahemaleptoceras,Chorizantheparryivar.parryi,andC.leptotheca.HabitatdiversityHabitatexpertsevaluatedalluvialscrubhabitatstohavelow-moderatephysicalandtopographicaldiversity,22moderatecomponentspeciesdiversity,23andlow-moderatefunctionalgroupdiversity.24Alluvialscrubisadaptedtoporoussubstrateswithlownutrientlevels,includingRiverwashAssociationsoils(mostcommonlyfoundalongriverchannelsandcomposedofsand,gravel,cobbles,andstones)andSobobaAssociationsoils(foundalongoutwashterracesandalluvialfansandcomposedofalluvium;Hanesetal.1989;NationalCooperativeSoilSurvey2015).Alluvialscrubhabitatsarestructurallycomplex(KirkpatrickandHutchinson1977).Localsiteconditionsandvariablefloodintervals,magnitudes,andintensitiesresultindifferentsuccessionalstagesofalluvialshrubvegetation(Hanesetal.1989;SaffordandQuinn1998;Smith1980;Wirka1997).Successionalstageshavebeendescribedaspioneer,intermediate,andmature(Smith1980),butlaterstudiesrecognizethesecategoriesastoosimplistic(BarbourandWirka1997;Buck-Diazetal.2011;Burketal.2007;Wirka1997).Generally,thereisaprogressioninvegetationcompositionobservedondifferentterraces,progressingoutwardandupwardfromthemorefrequentlyfloodedwashchannel(Burketal.2007;Hanesetal.1989).Pioneerspeciesaretypicallysparselylocatedintheyoungerandmoreactivelyfloodedlocations,andincludescalebroomandCaliforniabuckwheat(BarbourandWirka1997;Burketal.2007).Intermediatecommunitiesincludeavarietyofdensesubshrubsanddrought-deciduousshrubs(Hanesetal.1989).Morematurecommunitiesassociatedwithanaccumulationoffinesoilparticlesincludefullydevelopedsubshrubsandlarger,long-livedevergreenwoodyshrubs(Burketal2007;Hanesetal.1989).However,successionishighly20Confidence:Moderate21AllinformationafterthiscitationalsocomesfromA.Montalvo,pers.comm.,2015,exceptwherenoted.22Confidence:High23Confidence:High24Confidence:High


11

variableatthesitelevel,andlong-establishedcommunitiescanincludevariabledensitiesofspeciesfromallthreesuccessionalstages(BarbourandWirka1997;Wirka1997).Alluvialscrubhabitatsarefloristicallydiverse(KirkpatrickandHutchinson1977;Wirka1997)andsupportadiversityofrareanimalspecies.Alluvialscrubvegetationtendstoincludemoremesicspeciesthanotherscrubhabitatsuchascoastalsagescrub.ScalebroomisthemainindicatorspeciesofmostalluvialscrubcommunitiesinsouthernCalifornia(Buck-Diazetal.2011),andisfoundinallsuccessionalstages(Hanesetal.1989),butsomeolderalluvialscrubplantcommunitiesonfinersubstrateslackscalebroom(BarbourandWirka1997;Buck-Diazetal.2011).InSanDiegoCounty,scalebroomtendstobereplacedbybroombaccharis(Baccharissarothroides)asanindicatorspecies(Smith1996).Othercommonalluvialscrubspeciesinclude:Californiabuckwheat,Californiasagebrush(A.californica),whitesage(Salviaapiana),deerweed(Acmisponglaber),pricklypear(Opuntiaspp.),yerbasanta(EridictyontrichocalyxandE.crassifolium),andchaparralyucca(Hesperoyuccawhipplei)(BarbourandWirka1997).Alluvialscrubcommunitiesalsofeaturediversecryptobioticsoilcruststhatincludelichens,mosses,liverworts,andcyanobacteriathatthriveduringwetperiods(Allen1996;Jigouretal.2001).Alluvialscrubhabitatscanalsoincludeannualspringwildflowers,chaparralanddesertspecies,andsomesmallriparianwoodlandspecies,thoughthelattergroupsaretypicallyfoundonlyinintermediateormaturevegetationcommunitiesandareoftenstunted(BarbourandWirka1997;Hanesetal.1989;Jigouretal.2001;SaffordandQuinn1998).AnalysisofsurveysofalluvialscrubcommunitiesfromtheSantaAnaRiverWatersheddetailedover438vascularplantspeciesandclassifiedvegetationinto10differentalliances25and12differentassociations(Buck-Diazetal.2011),demonstratingthediversityandspeciesrichnessofthishabitattype.Somespecieswithinalluvialscrubhabitatsmaybemorevulnerabletoclimatechangeimpacts.Forexample,annualspeciesandshort-livedperennialsarelikelymorevulnerabletoannualclimaticfluctuationsduetoshortlifespans(VulnerabilityAssessmentReviewers,pers.comm.,2015).Otherspeciesmayalsoexperienceenhancedvulnerabilityduetocurrentthreatenedorendangeredstatus.Forexample,twoalluvialscrubspecies,theSantaAnaRiverwoolly-star(Eriastrumdensifoliumspp.sanctorum)andslender-hornedspineflower,areclassifiedasendangeredspeciesandareendemictoonlyafewwatershedsofsouthernCalifornia(Allen1996;AtallahandJones2003;BarbourandWirka1997;BrunellandRieseberg1993;Hanesetal.1989;Sclafani2013;WoodandWells1996).Limiteddistributionandpopulationsizesmakethesespeciesvulnerabletochangesinfloodregimesanddepositionpatternsintheircurrenthabitatarea.Inaddition,somepopulationsofthesespeciesarelocatedinareasprioritizedforhumanuse(e.g.,mining,percolationpondconstruction;VulnerabilityAssessmentReviewers,pers.comm.,2015).Additionally,thealluvialscruballianceL.squamatumisrankedasG3:S3bytheCaliforniaDepartmentofFishandWildlife(CaliforniaDepartmentofFishandWildlife[CDFW]2010),indicatingthatthisassociationisrareandthreatenedthroughoutitsrange,andhighlyimperiledwithinthestate(CDFW2015).

25Anallianceisdefinedas“agenericunitthatisusuallyrepresentedbydominantand/orcharacteristicplantspeciesintheupperlayerofvegetation”(Buck-Diazetal.2011).


12

ManagementpotentialHabitatexpertsevaluatedalluvialscrubhabitatstobeofmoderate-highsocietalvalue.26Alluvialscrubhabitatsarevaluedfortheiraesthetics,recreationalopportunities(e.g.,hiking),rarespecies,andastribalculturalandarchaeologicalsites(VulnerabilityAssessmentReviewers,pers.comm.,2015).Alluvialscrubhabitatsprovideavarietyofecosystemservices,including:biodiversity,watersupply/quality/sedimenttransport,recreation,carbonsequestration,andfloodanderosionprotection(VulnerabilityAssessmentReviewers,pers.comm.,2015).

Habitatexpertsrankedthepotentialformanagingoralleviatingclimateimpactsonalluvialscrubhabitatsasmoderate-high.27Habitatexpertsidentifiedthefollowingactionsaspotentialmanagementoptionsforalluvialscrubhabitats,butcommentedthatactionstakenwilldependlargelyondirectionandrateofclimatechanges:maintenanceofwaterflowthroughhabitat;removalofstructures(dams/levees)thatconstrictflowsoraffectsedimenttransport;structuraladditionstoslowflowvelocity;habitatrestorationandrevegetation;invasivespeciesmonitoringandremoval;andprotectionofalluvialscrubthrougharchaeological/culturalsiteprotection.SaffordandQuinn(1998)alsooutlinedpotentialmanagementstrategiesforalluvialscrubhabitats,including:maintainingconnectivityofoutwashfans;maintainingintactalluvialscrubhabitatwithminimalornohumandisturbance;maintainingfireandfloodingregimes;limitingdevelopmentinalluvialfans;andpreserving/maintainingasmanydistinctalluvialscrubstandsaspossible.

RecommendedCitationReynier,W.A.,L.E.Hillberg,andJ.M.Kershner.2017.SouthernCaliforniaAlluvialScrubHabitats:ClimateChangeVulnerabilityAssessmentSynthesis.Version1.0.EcoAdapt,BainbridgeIsland,WA.

ThisdocumentisavailableonlineattheEcoAdaptwebsite(http://ecoadapt.org/programs/adaptation-consultations/socal).

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(Dodecahemaleptoceras):Ecologicalanalysis.FinalreporttotheCaliforniaDepartmentofFishandGame.Riverside,CA:UniversityofCalifornia,Riverside.Retrievedfromhttps://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=3123

Barbour,M.G.,&Wirka,J.(1997).ClassificationofalluvialscrubinLosAngeles,RiversideandSanBernardinoCounties.Retrievedfromhttps://nrm.dfg.ca.gov/FileHandler.ashx?DocumentID=3125

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26Confidence:Moderate27Confidence:Moderate


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Alluvial'Scrub'Habitats'–'Overview'of'Vulnerability'Component'Evaluations'

Overall'Vulnerability'Ranking:1'4'ModerateDHigh' ' Overall'Confidence:2'3'High'

!SENSITIVITY'Sensitivity'Factor3' Sensitivity'Evaluation4' Confidence4'Sensitivities!to!Climate!&!Climate/Driven!Factors!

• Precipitation+• Soil+moisture+• Low+stream+flows+• Extreme+events:+drought+• Air+temperature+• Snowpack+depth+• Timing+of+snowmelt+&+runoff+• Extreme+events:+high+temperature+• Extreme+events:+low+temperature+• High!lentic/lotic!temperature5!• Other!(sediment!transport)5!

Overall:'4'ModerateDHigh'''

• 5!High!• 5!High!• 5!High!• 5!High!• 2!Low/Moderate!• 2!Low/Moderate!• 2!Low/Moderate!• 2!Low/Moderate!• 2!Low/Moderate!• 3!Moderate!• 5!High!

Overall:'2'Moderate'''

• 3!High!• 3!High!• 3!High!• 3!High!• 2!Moderate!• 2!Moderate!• 2!Moderate!• 2!Moderate!• 1!Low!• 2!Moderate!• 3!High!

Disturbance!Regimes!• Wildfire+• Flooding+• Wind5!• Insects5!• Disease5!

Overall:'2'LowDModerate''• 4!Moderate/High!• 2!Low/Moderate!• 1!Low!• 1!Low!• 2!Low/Moderate!

Overall:'2'Moderate'• 2!Moderate!• 2!Moderate!• 2!Moderate!• 2!Moderate!• 2!Moderate!

Non/Climate!Stressors!–!Degree!Stressor!Affects!Sensitivity!

• Dams+&+water+diversions+• Invasive+&+other+problematic+species+• Energy!production!&!mining5!• Transportation!corridors5!• Land!use!conversion5!• Recreation5!

Overall:'5'High''

• 5!High!• 4!Moderate/High!• 5!High!• 5!High!• 5!High!• 3!Moderate!

Overall:'3'High''

• 3!High!• 2!Moderate!• 3!High!• 2!Moderate!• 3!High!• 2!Moderate!

Non/Climate!Stressors!–!Current!Exposure!to!Stressor!

!

• Dams+&+water+diversions+• Invasive+&+other+problematic+species+

Overall:'5'High''

• 5!High!• 2!Low/Moderate!

Overall:'3'High''

'

• 3!High!• 2!Moderate!

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!1!Overall!vulnerability!is!calculated!according!to!the!following!formula:!Vulnerability!=!Sensitivity!*!(0.5*Exposure)!/!Adaptive!Capacity.!

2!Overall!confidence!is!an!average!of!the!overall!averaged!confidences!for!sensitivity,!exposure,!and!adaptive!capacity.!

3!Factors!with!expert!consensus!are!italicized;!all!other!factors!indicate!the!percentage!of!experts!who!identified!that!factor!as!important!to!consider!for!the!habitat.!

4!Scores!presented!reflect!an!average!of!all!scores!given!by!habitat!experts!for!a!given!factor.!5!Identified!by!50%!of!habitat!experts.!


16

Sensitivity'Factor3' Sensitivity'Evaluation4' Confidence4'• Energy!production!&!mining5!• Transportation!corridors5!• Land!use!conversion5!• Recreation5!

• 5!High!• 5!High!• 5!High!• 3!Moderate!

• 3!High!• 3!High!• 3!High!• 3!High'

Other!Sensitivities:!none!identified! N/A! N/A!

Overall'Averaged'Ranking'(Sensitivity):6'4'ModerateDHigh'

Overall'Averaged'Confidence'(Sensitivity):7'3'High'!

EXPOSURE'

Exposure'Factor3' Exposure'Evaluation4' Confidence4'Future!Climate!Exposure!Factors!

• Changes+in+precipitation+• Decreased+soil+moisture+• Altered+stream+flows+• Extreme+events:+increased+drought+• Increased+air+temperature+• Increased+wildfire+• Decreased!snowpack5!• Earlier!snowmelt!&!runoff5!• Extreme!events:!high!flows!&!runoff5!• Extreme!events:!high!temperatures5!• Extreme!events:!low!temperatures5!

Overall:'5'High'• 5!High!• 5!High!• 5!High!• 5!High!• 4!Moderate/High!• 4!Moderate/High!• 5!High!• 5!High!• 5!High!• 5!High!• 5!High!

Overall:'3'High'• 3!High!• 3!High!• 3!High!• 3!High!• 3!High!• 2!Moderate!• 3!High!• 3!High!• 3!High!• 3!High!• 3!High!

Overall'Averaged'Ranking'(Exposure):6'5'High'

Overall'Averaged'Confidence'(Exposure):7'3'High'!

ADAPTIVE'CAPACITY'Adaptive'Capacity'Factor' Adaptive'Capacity'Evaluation4' Confidence4'Habitat!Extent,!Integrity!&!Continuity!

• Geographic!Extent!!!

• Structural!&!Functional!Integrity!!!

• Habitat!Continuity!

Overall:'2'LowDModerate'• 2!Low/Moderate!

(Habitat!is!quite!limited!in!the!study!area)!

• 1!Low!(Isolated!and/or!quite!fragmented)!

• 2!Low/Moderate!(Only!some!habitat!patches!are!connected)!

Overall:'2'Moderate'• 3!High'

!'

• 2!Moderate!!!

• 2!Moderate'

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!6!Overall!averaged!ranking!is!an!average!of!the!sensitivity,!adaptive!capacity,!or!exposure!evaluation!columns!above.!

7!Overall!averaged!confidence!is!an!average!of!the!confidence!column!for!sensitivity,!adaptive!capacity,!or!exposure.!


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Adaptive'Capacity'Factor' Adaptive'Capacity'Evaluation4' Confidence4'Landscape!Permeability3!

Key!barriers:!• Energy+production+&+mining+• Dams+&+water+diversions!• Geologic+features+• Transportation!corridors5!• Land!use!conversion5!

Overall:'2'LowDModerate'Impact!on!landscape!permeability:!

• High!• High!• Moderate/High!• Moderate!• Low/Moderate!

Overall:'3'High''

• 3!High!• 3!High!• 3!High!• 2!Moderate!• No!answer!

given!Habitat!Resistance!&!Recovery!

• Resistance!• Recovery!

Overall:'3'Moderate'• 3!Moderate!• 4!Moderate/High!

Overall:'2'Moderate'• 2!Moderate!• 2!Moderate!

Habitat!Diversity!• Physical/Topographical!Diversity!• Component!Species!Diversity!• Functional!Group!Diversity!

Overall:'2'LowDModerate'• 2!Low/Moderate!• 3!Moderate!• 2!Low/Moderate!

Overall:'3'High'• 3!High!• 3!High!• 3!High!

Management!Potential!• Habitat!Value!• Likelihood!of!Managing!or!

Alleviating!Climate!Impacts!

Overall:'4'ModerateDHigh'• 4!Moderate/High!• 4!Moderate/High!

Overall:'2'Moderate'• 2!Moderate!• 2!Moderate'

Other!Adaptive!Capacities:!none!identified! N/A' N/A!

Overall'Averaged'Ranking'(Adaptive'Capacity):6'3'Moderate'

Overall'Averaged'Confidence'(Adaptive'Capacity):7'3'High'!

!!!!! !


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southern california alluvial scrub habitats -...

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